It is never too late to back out or say no. If you feel uncomfortable, let your partner know. Even if you have just started the process, you can stop at any time you want. Never feel pressured to continue. If you are with the right partner, he or she will respect your wishes.
Technically, it is never too late to say no but if you're being pressured you might want to have a back-up plan like get 911 or a trusted adult on speed dial, grip your car keys tighter, find a trusted friend, etc. Just in case said person who is pressuring you tries to push you to do something you don't want to.
